ISSN:1025-6016    

DOI:10.1080/10256010008032927

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A technical mixture of isomeric nonylphenols NP is formed as rather persistent degradation product of nonionic surfactants and has become widespread in the environment,e.g., in surface waters. Information about possible pathways for incorporation is needed for risk assessments, as NP has estrogenic properties. NP uptake after skin contact was determined using isolated and perfused bovine udders as models for human skin. NP-d2labelled in the positions ortho to the OH-group was prepared by an exchange procedure which did not measureably change the relative amount of isomers. Samples of udder perfusate, milk equivalent produced during the experiments and skin tissue were taken immediately before administration of 500 mg or 50 mg NP-d2on an udder skin area of 200cm2and then for 5 h. They were analyzed by GC-MS for NP and NP-d2after cleanup by steam distillation and final extraction with SPME fibres. The results are an unambiguous proof of the penetration of NP into the capillary system of living mammals after skin contact.

ISSN:1025-6016    

DOI:10.1080/10256010008032928

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Hyperoxaluria is the most important risk factor for a formation of calcium oxalate-urinary stones. Usually, the bulk of oxalate will be formed in the human body, but in many patients the oxalate from food plays the decisive role. Conventionally, in urine the endogenous oxalate can not be distinguished from food derived oxalate. We have developed a standardized oxalate-absorption test, applying a physiological dose (50 mg disodium salt of [13C2]oxalic acid) of labelled oxalate. The assay has been published. Now we report on the first extensive applications of this test in 86 volunteers and 135 patients from different groups with calcium oxalate stones or an increased risk of the formation of such stones. In one-third of the patients with calcium oxalate-urinary stones an oxalate hyperabsorption was diagnosed. For these patients, a dietetic stone prophylaxis and/or therapy is indicated.

ISSN:1025-6016    

DOI:10.1080/10256010008032929

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The nitrogen transfer between alfalfa and ryegrass was studied through isotope dilution at three different levels of N fertilization (20 mg N/pot, 200 mg N/pot, 400 mg N/pot) in a pot experiment using quartz sand as a substrate. An isogenic, nodulating, but non nitrogen fixing alfalfa line was used as a reference crop. Fixed N was transferred to the grass in the 20 mg N treatment and contributed markedly to the N nutrition of the grass (about 50% of the N in the plants). No transfer of fixed N could be detected in the higher fertilized treatments, although nitrogen fixation was only slightly inhibited by the presence of the fertilized mineral N. It is concluded that N transfer is strongly influenced by the N concentration in the substrate and transferred N contributes only slightly to the productivity of the legume/grass mixture under the given experimental conditions.

ISSN:1025-6016    

DOI:10.1080/10256010008032930

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The study of natural isotopic abundance signatures is useful to gain further insights in the processes resulting in depthwise changes in the composition of soil organic matter (SOM). Objectives were to describe the 6I3C and 6I5N abundances of SOM with depth in soils from a 153-year old beech (Bl), a 119-year old spruce (Fl) and a 61-year old spruce (F2) stand at Solling, north-west Germany, and to study, how podzolisation affects the isotopic abundances of I3C and I5N in the SOM. The degree of podzolisation decreased in the order F1> B1 > F2. At the surface of the humus layer of all three sites, 6I3C values are approximately 1 to 4OmO higher than in the leaves and needles, probably mainly due to the discrimination of I3C by microbial decomposition. I3C abundances in the organic layers of B1 and F2 increased only slightly from -27.6OmO PDB (Bl, L) to -27.2OmO PDB (Bl, Oh) and from -26.3% PDB (F2, L) to -25.9% PDB (F2, Oh), suggesting that biotic activity resulted in mixing of organic matter. At F1, however, I3C abundance increased from -27.5%0 PDB (L) to -26.0?? PDB (Oh) which reflects the lack of mixing by animals. In the upper 2-4cm of the mineral soil, i.e., in the eluvial horizons Aeh, I3C values showed a minimum at the spruce sites which was presumably related to translocation of I3C enriched fulvic acids. Depthwise changes in 6″N values were not related to podzolisation processes. At all three sites, a N enrichment with depth occurred in the mineral soil which is the result of the discrimination of I5N by microbial decomposition.

ISSN:1025-6016    

DOI:10.1080/10256010008032931

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The dynamics of C and N in terrestrial ecosystems are not completely understood and the use of stable isotopes may be useful to gain further insight in the pathways of CO2emissions and leaching of dissolved organic carbon (DOC) and nitrogen (DON) during decomposition of litter. Objectives were (i) to study the decomposition dynamics ofCalamagrostis epigeios, a common grass species in forests, using13C-depleted and15N-enriched plants and (ii) to quantify the effect wood ash addition on the decomposition and leaching of DOC and DON. Decomposition was studied for 128 days under aerobic conditions at 8°C and moisture close to field capacity in a spodic dystric Cambisol with mor-moder layer. Variants included control plots and additions of (i)Calamagrostislitter and (ii)Calamagrostislitter plus 4 kg ash m−2.1.Decomposition ofCalamagrostisresulted in a CO2production of 76.2 g CO2–C m−2(10% of added C) after 128 days and cumulative DOC production was 14.0 g C m−2out of which 0.9g C m−2wasCalamagrostis-derived (0.1% of added C). The specific CO2formation and specific DOC production fromCalamagrostiswere 6 times higher (CO2) and 4 times smaller (DOC) than those from the organic layer. The amount ofCalamagrostis-derived total N (NH4+, NO3−, DON) leached was 0.7g N m−2(4.8% of added N). Cumulative DON production was 0.8g N m−2which was slightly higher than for the control. During soil passage, much of the DOC and DON was removed due to sorption or decomposition. DOC and DON releases from the mineral soil (17cm depth) were 6.3g C m−2and 0.5g N m−2.Addition of ash resulted in a complete fixing of CO2for 40 days due to carbonatisation. Afterwards, the CO2production rates were similar to the variant without ash addition. Production of DOC (98.6g C m−2) and DON (2.5g N m−2) was marked, mainly owing to humus decay. However, Calamagrostis-derived DOC and Culamagrostis-derived total N were only 3.9g C m−2(0.5 YO of added C) and 0.5g N m−2(3.4% of added N). The specific DOC production rate from the organic layer was 6 times higher than that from Cularnagrostis. The results suggest that with increasing humification from fresh plant residues to more decomposed material (OFand OHlayers) the production ratio of DOC/CO2-C increases. Addition of alkaline substances to the forest floor can lead to a manifold increase in DOC production.

ISSN:1025-6016    

DOI:10.1080/10256010008032932

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A continuous dual13CO2and15NH415NO3labelling experimental set-up is presented that was used to investigate the C and N uptake and allocation within 3-year old beech (Fagus sylvaticaL.) during one growing season. The C and N allocation pattern was determined after six, twelve and eighteen weeks of growth. The carbon uptake was distinctly different in the three phases examined: The first six weeks after budbreak were dedicated to leaf growth with aR/S(root to shoot) ratio of 0.14 for the new carbon. The second growth phase showed a balancedR/Sratio of C allocation and after week 13, the root compartment was the main carbon sink (R/S= 6.97).

ISSN:1025-6016    

DOI:10.1080/10256010008032933

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

One purpose of new land use concepts for degraded fens (organic soils with high N content) is the reduction of the mineralization process due to very high groundwater levels. However, knowledge of nitrogen mineralization process (net and gross) in degraded fen soils affected by reflooding is very small. Therefore, the objectives of our study were (a) to evaluate the suitability of15N pool dilution method for measurements of gross mineralization rates in degraded fen soils and (b) to investigate how the reflooding of a degraded fen affects the net and gross nitrogen mineralization in a short-term incubation experiment. The usability of the15N pool dilution method was diminished by the low recovery of the applied15NH4−at time zero. The recovery of the added15NH4−in the extractable soil NH4−pool was only 13.5% for the drained soil and 59.6% for the reflooded soil. However, the gross mineralization rates were similar for both soils and exceeded always the net rates substantially. The cumulative net mineralization rate was higher for the reflooded soil (1.58 μg N*cm−3*d−1) than for the drained soil (-0.67 μg N*cm−3*d−1). Differences between the two soils were also found in the nitrification intensity and the loss of15N. This was probably one reason for the higher net mineralization rate in the reflooded soil.

ISSN:1025-6016    

DOI:10.1080/10256010008032934

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

This is a scanned image of the original Editorial Board page(s) for this issue.

ISSN:1025-6016    

DOI:10.1080/10256010008032926

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor